Once-through vapor generator furnace buffer circuit



Oct. 3, 1967 w. P. GORZEGNO ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFERCIRCUIT 3 Sheets-Sheet 1 Filed Oct. 22, 1965 lNVENTOR WAIT/F1? PGORZEG/VO ATTORNEY Oct. 3, 1967 ONCE-THROUGH VAPOR GENERATOR FURNACEBUFFER CIRCUIT Filed Oct. 22, 1965 3 Sheets-Sheet 2 U1 5 gIZO Z I U] E 0MI 1::

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INVENTOR WAL 767? f GORZEG/VO BY @4144, A PZ ATTORNEY Oct. 3, 1967 w. P.GORZEGNO 3,344,777

ONCE-THROUGH VAPOR GENERATOR FURNACE BUFFER CIRCUIT Filed Oct. 22, 19653 Sheets-Sheet 5 Fig.5

er to Pass 4 INVENTOR WAL 75,? F? GO/QZEG/VO ATTORNEY United StatesPatent Ofiiice 3,344,777 Patented Oct. 3, 1967 3,344,777 ONCE-THROUGHVAPOR GENERATOR FURNACE BUFFER CIRCUIT Walter P. Gorzegno, Florham Park,N.J., assignor to Foster Wheeler Corporation, New York, N.Y., acorporation of New York Filed Oct. 22, 1965, Ser. 501,168 6 Claims. (Cl.122-406) ABSTRACT OF THE DISCLOSURE A forced-flow once-through vaporgenerator wherein the furnace is an all-welded enclosure comprising aplurality of upright tube panels welded together, each of the tubepanels having parallel tubes welded together. The panels are seriallyconnected, with panels at different temperature levels being separatedfrom each other by an intermediate panel. The fluid entering theintermediate panel is a mixture of the fluids entering the separatedpanels.

This invention relates to a forced-flow supercritical or subcriticalonce-through vapor generating unit.

A vapor generating unit, of the type to which the present invention isapplicable, is described in co-pending application, Ser. No. 370,604,filed May 27, 1964, by Walter P. Gorzegno et al.

In this type of a unit, the furnace wall enclosure is divided verticallyinto upper and lower portions, the lower portion constituting a hightemperature radiant heat zone contaning the burners for the unit. Thelower portion itself is divided peripherally into a plurality of passsections, each pass section comprising parallel finned tubes weldedalong their lengths into vertically oriented sideby-side panels. Inletand outlet headers serve each pass section separately, and are connectedso that the flow in the lower enclosure wall is in series through thesuccessive pass sections. From the lower portion of the furnace and passsections therefor, the fluid flows to the upper portion constituting atleast one additional flow pass in the furnace area.

The circuits in both the upper and lower portions of the furnace aredivided into as many passes as the needed to meet minimum velocity andenthalpy pick-up requirements. Since the burners are located in thevicinity of the lower passes, where high local heat inputs can beexpected, the lower portion of the furnace is generally provided with agreater number of passes than the upper portion.

The arrangement offers many advantages. Flow is always up in the furnacetubes. Frequent mixing resulting in low fluid anthalpy pick-up for acircuit gives good circuit characteristics and eliminates the need forusing orifices for uniform distribution of flow. A desired flexibilityin design is available, and the use of excessively small diameter tubes,subject to plugging, is avoided.

Since the enthalpy of the fluid increases from pass to pass in thefurnace periphery, a temperature differential exists between passes. Ifthe tubes of one pass panel are welded directly to those of another, thehigher the temperature differential, the higher the stresses will be inthe panel joints. It is advantageous to provide a means to reduce thesestresses to lowest levels.

In accordance with the invention, this means is provided, in aonce-through vapor generator which includes a plurality of thevertically oriented adjacent tube panels welded together into agas-tight enclosure, a header means connecting the panels so that thefluid makes successive flow passes in the generator with the panels ofsuccessive passes remote from each other, and at least one additionalheader arrangement adapted to transmit predetermined portions of theflow from the inlet ends of said remote panels to a panel intermediatethe remote panels. The intermediate panel, which can be termed a bufferpass, thus contains a mixture of fluid taken from the two successivepasses and is at an average temperature intermediate those of thesuccessive passes. In practice, a temperature differential exists,between adjacent welded tubes of the in-series pass panels and the panelof the buffer pass, less than F., a generally accepted limit based onweld and tube strength design criteria.

The invention and advantages thereof will become more apparent onconsideration of the following description, and accompanying drawings inwhich:

FIGURE 1 is an oblique view of a portion of a forced flow once-throughvapor generator illustrating the invention;

FIGURE 2 is a schematic diagram of the generator of FIG. 1 illustratingthe invention;

FIGURE 3 is a reduced size schematic oblique diagram illustrating thefull furnace circuitry and invention of the generator of FIG. 1;

FIGURE 4 is a load versus differential temperature graph illustratingadvantages of the invention; and

FIGURE 5 is a cross-section elevation view of the generator of FIG. 1.

eferring to FIGS. 1 and 5, the vapor generator furnace is of theflat-bottom type with fluid from an economizer (not shown) passingthrough a floor pass 12 of the generator to an outlet header 14 parallelto the front wall 16 of the furnace. From the header l4, risers 18transmit the partially heated fluid to an inlet header 20, which feedsthe tubes of a panel 22 making up the middle portion of the front wall16. The tubes of this panel constitute the furnace second pass, thefloor panel being a first pass. The tubes of panel 22 exit in an upperheader in the front wall (not shown in FIG. 1) and the fluid from thisheader is transmitted by parallel downcomcrs 24 to L-shaped headers 26in opposite front corners of the furnace periphery. These headers feedthe tubes of L-shap-ed panels 28 (also in the front corners of thegenerator) constituting pass 3 for the furnace circuitry.

It is apparent that the tube of pass 2 will be at a temperaturedifferent from those of pass 3. Since the furnace tubes are weldedtogether along their lengths to form a gas-tight enclosure, a stresswould be set up in the joint between passes 2 and 3 if the tubes ofthese passes were joined together. To reduce this thermal stress, abuffer circuit is provided comprising headers 30 positioned on oppositesides of the front wall second pass header 20, between this header andthe L-shapcd headers 26 for pass 3. On opposite sides of the second passpanel 22 between this panel and the panels 28 for the third pass, buffercircuit panels 32 receive fluid from the headers 30. The buffer circuit,comprising the headers 30 and panels 32, receive fluid from the secondpass downcomers 24 (or third pass inlet) via small diameter lines 34,and also receive fluid from risers 18, or the second pass inlet, throughorifice valves 36. By proper proportioning of the lines 34 and orificevalves 36, the buffer circuit receives predetermined proportions offluid from the inlet ends of both passes 2 and 3, to attain atemperature which is intermediate the temperatures of the pass 2 and 3circuits.

The remainder of the side walls and the rear wall of the furnaceenclosure are made up of tubes of a pass No. 4 (item 40), receivingfluid from pass No. 3 via the U- shaped header 42. The dimensions ofpass No. 4 are consideraly greater than those of prior passes, toaccommodate design requirements.

Butler circuits could also be disposed between the tubes of passes 3 and4. However, in this example, the passes are sized in such a way that thetemperature differential between these two passes is substantially lessthan 100 R, an accepted limit, obviating the need for the buffercircuit.

FIGURE 2 provides a clear illustration of the fluid flow in the furnacecircuitry. From the downcomer and floor pass 1, the fluid is transmittedto the pass No. 2 header, designated item 20. Downcotners 24 transmitthe pass No. 2 flow to headers 26 for pass No. 3. At connections 44 and46, predetermined proportions of the flows to both pass Nos. 2 and 3 aretransmitted to the butter circuit passes, items 32. Orifices 36 and linesizing establish the proportions obtained. The proportions of each floware usually kept at 50-50. The butler circuit outlet corresponds to theoutlet of pass 3, and the fluid is then transmitted to pass No. 4, notshown in FIG. 2.

From pass No. 4, the fluid follows the circuitry set forth in theco-pending application mentioned above, being transmitted to a U-shapedpass No. 5 making up the entire front and side wads of the upper part ofthe furnace. This is shown in FIG. 3, connections 48 serving to transmitthe flow.

As a general rule, the buffer circuit will comprise at least 5% of thetubes in the applicable wall width to achieve a practical reduction ofjoint longitudinal thermal stress. A typical temperature differentialbetween passes 2 and 3 may be in the range from 100 F. to 135 F. By useof the buffer circuit, the temperature differential be tween tubes atthe joint will be reduced in half. Experimental stress analyses haveshown that longitudinal thermal stresses between tube vertical jointsare reduced by approximately when the butter circuit is about 12.5% ofthe total panel width. Geometry is im portant, the more tubes employedin the buffer circuit for a constant wall dimension, the greater will bethe reduction in longitudinal thermal stress.

FIG. 4 is from a particular example in accordance with the invention.The graph shows that the largest temperature differentials occur atload. With a maximum pass 2 and a pass 3 temperature differential ofabout 106 F.. a butler circuit of 1?. tubes was used. Headers for thebuffer circuit provided an equal flow from both passes 2 and 3.sufficient to have the same flow in pounds per hour-tube as in passes 2and 3. This resulted in a temperature differential of 50 F. between thebuffer circuit inlet and the pass 2 and 3 inlets, at 30% load. For thegeometry involved, that is, buffer circuit width vs. Wall applicablewidth, a 15% reduction in joint longitudinal thermal stress ispredicted.

Although the invention has been described with respect to specificembodiments, many variations within the spirit and scope of theinvention as defined in the following claims will be apparent to thoseskilled in the art.

What is claimed is:

1. A once-through vapor generator which includes a plurality of parallelvertically oriented tubes welded into laterally adjacent panels todefine an essentially gas-tight furnace enclosure, and header meansconnecting panels laterally remote from each other to define at leasttwo upfiow flow passes in series so that fluids entering said panels areat different enthalpies, the improvement comprising at least oneadditional header means connected to the panel intermediate said remotepanels; and

means for transmitting to said additional header means predeterminedportions of the flow to said remote panels, the enthalpy of the fluidentering said intermediate panel thereby being intermediate theenthalpies of the fluids entering said remote panels.

2. A once-through vapor generator comprising a rectangular verticallyoriented furnace enclosure; the enclosure comprising sideby-side panelsections defining a plurality of laterally adjacent upflow flow passes;each panel section comprising parallel vertically oriented finned tubeswelded together along their lengths; the panel sections being weldedtogether lengthwise thereof so that the enclosure is essentially gastight; burner means radiantly heating said enclosure; header meansconnecting at least two of the flow passes in series, the enthalpy ofthe fluid increasing in the Successive passes; and second header meansadapted to receive predetermined portions of the flow from the inletends of both said flow passes and to mix and feed said portions to apass the tubes of which define a panel section intermediate the panelsections of said two flow passes. 3. A once-through vapor generatorcomprising a rectangular vertically oriented furnace enclosure havingfront, rear and side walls; the enclosure being divided vertically intoupper and lower portions; burner means in the lower portion front andrear walls radiantly heating said enclosure; the lower portion of theenclosure comprising a plurality of side-by-side panel sections eachpanel section comprising tubes welded together along their lengths, thepanel sections being welded together lengthwise thereof so that theenclosure is essentially gas tight; header means connecting the panelsections into at least three successive flow passes in series wherebythe first pass constitutes a portion of the front wal the third passconstitutes portions of the side walls and the rear Wall, and the secondpass constitutes portions of the front and side walls in the frontcorners of the enclosure, the panels being sized so that the temperaturedifference between the first and second flow passes is more than F.; theenclosure comprising two buffer panel sections inter mediate the panelsection for the first pass and those for the second pass; and secondheader means adapted to receive and mix predetermined portions of theflow from the inlet ends of the first and second passes and to pass saidportions to the inlet ends of said buffer panel sections. 4. Aonce-through vapor generator according to claim 3 wherein the panels aresized such that the temperature difference between the second and thirdpass inlets is less than 100 F.

5. A once-through vapor generator according to claim 4 wherein at leastone additional upflow pass comprises the side and rear walls of thelower portion of the furnace enclosure, and header means connecting thethird pass to said additional upflow fluid pass, the passes one to fourbeing progressively larger in number of tubes with increasing enthalpyof the fluid flow.

6. A once-through vapor generator according to claim 3 wherein thebuffer panel sections comprise at least 5% of the tubes in theapplicable wall width.

References Cited UNITED STATES PATENTS CHARLES I. MYHRE, PrimaryExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,344,777 October 3, 1967 Walter P. Gorzegno It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1 line 33 "contaning" should read containing line 45 "the",second occurrence should read are line 54 "anthalpy" should readenthalpy Column 2 line 45 "tube" should read tubes Column 3, line 42after "and" cancel "a"; line 47 "50 F. should read 53 F. line 62, after"thgf" cl'lnsert the Column 4 line 53 after "upflow" insert H u1 Signedand sealed this 29th day of July 1969 (SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,344,777 October 3, 1967 Walter P.Gorzegno It is certified that error appears in the above identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 33, "contaning" should read containing line 45, "the",second occurrence, should read are line 54, "anthalpy" should readenthalpy Column 2, line 45, "tube" should read tubes Column 3, line 42,after "and" cancel "a"; line 47, "50 F." should read 53 F. line 62,after "thafif'wiinsert the Column 4, line 53, after "upflow" insert L11--f.

Signed and sealed this 29th day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM Attesting Officer Commissioner ofPatents

1. A ONCE-THROUGH VAPOR GENERATOR WHICH INCLUDES A PLURALITY OF PARALLELVERTICALLY ORIENTED TUBES WELDED INTO LATERALLY ADJACENT PANELS TODEFINE AN ESSENTIALLY GAS-TIGHT FURNACE ENCLOSURE, AND HEADER MEANSCONNECTING PANELS LATERALLY REMOTE FROM EACH OTHER TO DEFINE AT LEASTTWO UPFLOW FLOW PASSES IN SERIES SO THAT FLUIDS ENTERING SAID PANELS AREAT DIFFERENT ENTHALPIES, THE IMPROVEMENT COMPRISING AT LEAST ONEADDITIONAL HEADER MEANS CONNECTED TO THE PANEL INTERMEDIATE SAID REMOTEPANELS; AND MEANS FOR TRANSMITTTING TO SAID ADDITIONAL HEADER MEANSPREDETERMINED PORTIONS OF THE FLOW TO SAID REMOTE PANELS, THE ENTHALPYOF THE FLUID ENTERING SAID INTERMEDIATE PANEL THEREBY BEING INTERMEDIATETHE ENTHALPIES OF THE FLUIDS ENTERING SAID REMOTE PANELS.